The present invention relates to rotary skiving knives and means for remotely actuating such knives.
Rotary skiving tools are used to accurately cut small quantities of material from the wall of a cylindrical hole. After the skiving tool has made a pass through the workpiece it is usually drawn back through the newly worked hole. If the knife blades on the skiving tool are not retracted the blades will scratch or score the surface of the hole. This is totally unacceptable when unmarred finishes are needed, for example in hydraulic cylinders.
Retractable rotary skiving knives have been developed so that the knife blades do not score the cylinder wall (see, for example, U.S. Pat. No. 3,795,957). These tools typically use a knife holder having two knife blades. The knife blades are pulled inwardly by springs and are extended by pulling (or pushing) a shifting rod having a tapered end, against which the knife blades rest, to wedge the knife blades apart. Pushing (or pulling) the shifting rod allows the springs to pull the blades inwardly so the tool can be withdrawn from the workpiece. The distance the blades extend is determined by the distance the shifting rod moves and the angle of the tapered end. With this arrangement the radial forces on the knife blades are transmitted from the knife blades to the shifting rod to produce axial forces on the shifting rod. The extended position of the knife blades can vary, possibly resulting in an out-of-tolerance hole, depending upon several factors including the ridigity with which the shifting rod is locked into place and the amount of relative movement which occurs between the mating surfaces of the tapered end of the shifting rod and the knife blades. Further, centrifugal forces on the rotating knife tend to urge the knife blades outwardly in opposition to the springs.
Skiving tools are often used in combination with a roller burnishing tool so that the skiving tool first cuts or shaves off a small amount of material from the hole and then the roller burnishing tool, mounted coaxially on the same drive shaft with the skiving tool, burnishes the hole to a smooth finish.
Roller burnishing tools utilize a plurality of circumferentially spaced rollers in a roller cage to roller burnish the interior of a pre-formed cylindrical hole so that it has a smooth finish. Tools of this type are available in which rollers are located on a race which is inclined radially outwardly toward the rear, and a manually adjustable stop is provided which restricts the rearward movement of the rollers up the inclined race. Tools utilizing roller burnishes of this type are illustrated in a brochure of the Hegenscheidt Corporation, having a U.S. office at 1070 Livernoise Ave., Troy, Mich. 48084 entitled The Combined Skiving and Roller Finishing Tools, Type RDS RETRAC, and U.S. Pat. Nos. 3,795,957 and 4,133,089.
When roller burnishing tools of the type described above are inserted in a cylinder, the forward thrust of the tool causes the rollers to move upwardly along the inclined race until the race contacts the preset stop. Accordingly, for all practical purposes, the rollers have a preset radius depending on the position of the stop.
If the diameter of the interior of a cylinder is very close to its nominal diameter, the roller burnishing operation will typically proceed quite smoothly. However, if the diameter of the cut cylinder is slightly oversized, the interior surfaces of the cylinder may not be sufficiently burnished. If the diameter is somewhat smaller than nominal, caused by cutting tool wear or other variables, the effective fixed diameter of the rollers will cause excessive working of the interior surfaces of the cylinder, requiring large forces to drive tht tool through the cylinder, and often resulting in jamming of the tool inside the cylinder. If jamming does occur, the tool often cannot be retrieved intact, resulting in destruction of an extremely expensive working tool.
A roller burnishing tool is typically inserted into the cylinder through a drawtube to align it with the interior of the cylinder. The drawtube has the same or nearly the same diameter as the cylinder, and the roller burnishing tool as described above will roller burnish the drawtube on each cycle. Eventually, the drawtube becomes oversized, and the diameter of the drawtube does not accurately match that of the cylinder. When the roller cage reaches the preset stop further outward movement of the roller is prevented, and the drawtube will not accurately align the tool with the cylinder.
The roller burnishing tools described above typically have nylon pads to stabilize the roller burnishing action of the tool. These nylon pads tend to wear with use, and when worn, often causing chattering of the tool, which ruins the cylinder finish. In addition, if the nylon pads are worn, the rollers may contact the interior surface of th cylinder when the tool is withdrawn and score the interior surface so that it is unusable.